diff --git a/custom_components/wundasmart/sensor.py b/custom_components/wundasmart/sensor.py
index f022e06..d7240e3 100644
--- a/custom_components/wundasmart/sensor.py
+++ b/custom_components/wundasmart/sensor.py
@@ -1,5 +1,6 @@
 """Support for WundaSmart sensors."""
 from __future__ import annotations
+from dataclasses import dataclass
 import itertools
 
 from homeassistant.core import HomeAssistant, callback
@@ -29,8 +30,15 @@ def _number_or_none(x):
         return None
 
 
-ROOM_SENSORS: list[SensorEntityDescription] = [
-    SensorEntityDescription(
+@dataclass
+class WundaSensorDescription(SensorEntityDescription):
+    available: bool | callable = True
+
+
+
+
+ROOM_SENSORS: list[WundaSensorDescription] = [
+    WundaSensorDescription(
         key="temp",
         name="Temperature",
         icon="mdi:thermometer",
@@ -38,7 +46,7 @@ def _number_or_none(x):
         device_class=SensorDeviceClass.TEMPERATURE,
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="rh",
         name="Humidity",
         icon="mdi:water-percent",
@@ -46,7 +54,16 @@ def _number_or_none(x):
         device_class=SensorDeviceClass.HUMIDITY,
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
+        key="temp_ext",
+        name="External Probe Temperature",
+        icon="mdi:thermometer",
+        available=lambda state: bool(int(state.get("ext", 0))),
+        native_unit_of_measurement=UnitOfTemperature.CELSIUS,
+        device_class=SensorDeviceClass.TEMPERATURE,
+        state_class=SensorStateClass.MEASUREMENT,
+    ),
+    WundaSensorDescription(
         key="bat",
         name="Battery Level",
         icon=lambda x: icon_for_battery_level(_number_or_none(x)),
@@ -54,7 +71,7 @@ def _number_or_none(x):
         device_class=SensorDeviceClass.HUMIDITY,
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="sig",
         name="Signal Level",
         icon=lambda x: icon_for_signal_level(_number_or_none(x)),
@@ -64,8 +81,8 @@ def _number_or_none(x):
     )
 ]
 
-TRV_SENSORS: list[SensorEntityDescription] = [
-    SensorEntityDescription(
+TRV_SENSORS: list[WundaSensorDescription] = [
+    WundaSensorDescription(
         key="vtemp",
         name="Temperature",
         icon="mdi:thermometer",
@@ -73,7 +90,7 @@ def _number_or_none(x):
         device_class=SensorDeviceClass.TEMPERATURE,
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="bat",
         name="Battery Level",
         icon=lambda x: icon_for_battery_level(_number_or_none(x)),
@@ -81,7 +98,7 @@ def _number_or_none(x):
         device_class=SensorDeviceClass.HUMIDITY,
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="sig",
         name="Signal Level",
         icon=lambda x: icon_for_signal_level(_number_or_none(x)),
@@ -89,27 +106,27 @@ def _number_or_none(x):
         device_class=SensorDeviceClass.HUMIDITY,
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="vpos",
         name="Position",
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="vpos_min",
         name="Position Min",
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="vpos_range",
         name="Position Range",
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="downforce",
         name="Downforce",
         state_class=SensorStateClass.MEASUREMENT,
     ),
-    SensorEntityDescription(
+    WundaSensorDescription(
         key="trv_range",
         name="TRV Range",
         state_class=SensorStateClass.MEASUREMENT,
@@ -202,10 +219,17 @@ def __init__(
         # Update with initial state
         self.__update_state()
 
+    @property
+    def available(self):
+        if callable(self.entity_description.available):
+            device = self.coordinator.data.get(self._wunda_id, {})
+            state = device.get("state", {})
+            return self.entity_description.available(state)
+        return self.entity_description.available
+
     def __update_state(self):
         device = self.coordinator.data.get(self._wunda_id, {})
         state = device.get("state", {})
-        self._attr_available = True
         self._attr_native_value = state.get(self.entity_description.key)
 
     @callback
diff --git a/tests/fixtures/test_get_devices1.json b/tests/fixtures/test_get_devices1.json
index 4923652..c89c694 100644
--- a/tests/fixtures/test_get_devices1.json
+++ b/tests/fixtures/test_get_devices1.json
@@ -23,8 +23,8 @@
                 "v": "1.8",
                 "temp": "17.8",
                 "rh": "66.57",
-                "temp_ext": "",
-                "ext": "0",
+                "temp_ext": "18.0",
+                "ext": "1",
                 "bat": "100",
                 "sig": "88",
                 "alarm": "0"
@@ -55,7 +55,7 @@
                 "t_norm": "19.00",
                 "t_hi": "21.00",
                 "heat": "4",
-                "temp_pre": "0",
+                "temp_pre": "4",
                 "prg": "1",
                 "lock": "0",
                 "temp": "0.00",
diff --git a/tests/test_sensor.py b/tests/test_sensor.py
index abefff4..ca07441 100644
--- a/tests/test_sensor.py
+++ b/tests/test_sensor.py
@@ -37,6 +37,10 @@ async def test_sensors(hass: HomeAssistant, config):
         assert trv_signal_state.state == "88"
         assert trv_signal_state.attributes["icon"] == "mdi:signal-cellular-3"
 
+        ext_temp_state = hass.states.get("sensor.test_room_external_probe_temperature")
+        assert ext_temp_state
+        assert ext_temp_state.state == "18.0"
+
     coordinator: DataUpdateCoordinator = hass.data[DOMAIN][entry.entry_id]
     assert coordinator